Gaia16aye

In astronomy, Gaia16aye is a gravitational microlensing event of the star 2MASS 19400112+3007533 (the source star) by a dimmer binary star system (the lens star system).[1] The source star 2MASS 19400112+3007533 is a magnitude 14.5 (Gaia RP) star in Cygnus. It was closely observed during a set of brightening events caused by gravitational microlensing in 2016.[2] The Gaia16aye event was first noticed by the Gaia space mission via an alert on August 9, 2016.[3][4] The unusual characteristics of the event led to an immediate massive follow-up campaign by tens of professional and amateur observers over the next 500 days, during which 5 brightening events were closely observed.[1] The star brightened up to two and a half magnitudes in each microlensing event over its baseline brightness.

The brightenings were determined to have been caused by a dim binary star system much closer to the Earth, acting as a moving, changing gravitational lens. The light of the lens star system itself was lost in the glare of the brighter star 2MASS 19400112+3007533. The lens star system is predicted to be observable in 2021 after its proper motion has created a separation of about 50 mas from the brighter background star. Detailed observations and analytical modelling determined that the lens system consists of two main sequence stars with Solar masses 0.57 ± 0.05 and 0.36 ± 0.03, at a distance of 780 pc (2,500 ly), and an orbital period of 2.88 years.[5]

The space-time geometry of a binary star system is complicated, which leads to sudden jumps in brightness as the caustics of the lens cross by the light rays from the lensed source.[4] Furthermore, the relative motions of the binary lens stars and the source star interacted with each other:

The rotation was fast enough and the overall micro-lensing event slow enough that the background star entered the high magnification region, left it and then entered it again

— Lukasz Wyrzykowski, Global Gaia campaign reveals secrets of stellar pair